The present invention relates in general to semiconductor devices and, more particularly, to monolithic transient voltage suppressor devices.
Transient voltage suppressors are used in a variety of electrical systems to prevent high voltage transients from damaging system components. For example, computer systems connect transient voltage suppressors across data and/or power lines to dissipate the energy induced by a transient event such as a noise pulse, a static discharge, or a lightning strike. The transient suppressors break down when a transient voltage exceeds a predetermined level, thereby limiting the voltage on the data and power lines and avoiding component damage. A typical transient suppressor breaks down when a transient voltage exceeds eight volts and shunts at least one ampere of current which would otherwise flow through other system components and lead to a destructive failure of the system.
Current transient voltage suppressors use large avalanche diodes to dissipate the current associated with the transient event. However, these avalanche diodes have the problem of high capacitance, which loads the data lines and slows down the data transfer rate. Other transient voltage suppressors reduce capacitance by coupling a low capacitance diode which is forward biased in series with the avalanche diode. Each diode is housed in a separate semiconductor package, which results in a high cost of manufacturing and using the suppressor. Yet other transient voltage suppressors mount both diodes in the same package and use wire bonds to interconnect the separate dice. Such a scheme reduces the cost of using the suppressors, but the manufacturing cost is still too high for many applications. Still other transient voltage suppressors are fabricated as punchthrough diodes in which the transient voltage depletes an entire doped region of a semiconductor die and xe2x80x9cpunches throughxe2x80x9d to an adjacent doped region. However, these devices have a low yield and high cost because of the difficulty in controlling both the doping level and distance across the doped region simultaneously. Moreover, punchthrough diodes have a high capacitance and therefore reduce system speed and performance.
Hence, there is a need for a transient voltage suppressor that is formed on a single semiconductor die to have a low cost and which has a low capacitance to maintain a high system performance.